Graphene is in the form of a two-dimensional crystal of carbon atoms and great attention has been focused on graphene as industrial material since its discovery in 2004. Graphene has excellent electric, thermal, optical, and mechanical characteristics, and there are growing expectations for its applications in wide areas such as production of battery materials, energy storage materials, electronic devices, and composite materials.
Methods available for the production of graphene include the mechanical exfoliation method, CVD (chemical vapor deposition) method, and CEG (crystal epitaxial growth) method. Among others, the oxidization-and-reduction method, in which graphite oxide or graphene oxide is produced first through oxidization of natural graphite, followed by converting it into graphene through reduction reaction, is now expected as a promising industrial method for large-scale production.
In Patent document 1, graphene oxide is expanded and exfoliated while it is heated for reduction in order to produce thin layers of graphite with a large specific surface area.
In Patent document 2, graphene is chemically reduced and subsequently freeze-dried to prepare a graphene powder with high dispersibility.
In Patent document 3, graphene powder is produced by applying ultrasonic waves to a liquid mixture containing graphite particles to prepare a graphene dispersion liquid and removing the dispersion medium by drying.